Image receiving sheet with a double pvahygroscopic salt layer coating



United States Patent 3,379,532 IMAGE RECEIVHNG SHEET WITH A DOUBLE PVA- HYGROS0PIC SALT LAYER COATlNG Rudolf Weudt, Hamburg, Germany, assignor to Lunloprint Zindier KG, Hamburg, Germany, a corporation of Germany No Drawing. Filed July 5, 1963, Sea. No. 293,186

4 Claims. (Cl. 96-76) ABSTRACT OF THE DISCLOSURE In the dry production or unreversed positive prints using silver-salt diffusion, an exposed photographic silverhalide-emulsion layer is heated upon juxtaposition thereof with an image-receiving layer containing, in addition to a conventional ditfused-silver-salt developer, a hygroscopic water-retentive salt from the group which consists of zinc chloride hemihydrate, lithium chloride monohydrate, potassium acetate, calcium chloride hexahydrate,

This invention relates to a process for the preparation of unreversed positive prints using a photographic silverhalide-emulsion layer containing developer substances, which layer, after exposure, is subjected to a heating step in contact with an image-receiving layer which contains a film former and reagent means, known in association with the silver-salt-diffusion process or proposed for effecting simultaneous production of the moisture necessary for carrying out silver-salt-diflusion and the known preparation of a silver image in the receptor layer. Also, the invention relates to a method of preparation of the sensitive material.

Diffusion processes are known in which by exposure, e.g., illumination, a latent image is produced in a photographic layer, which is then moistened with a fluid developer. This latent image is then developed in contact with a gelatin layer containing reduction nuclei, preferably colloidal silver, by dissolution of the unexposed silver halide.

It has been proposed to include in the receptor layer, for improving the transmission or diffusion capacity, apart from substances for dissolving the silver halide (sodium thiosulphate, for example), reagents which form.

difiicultly soluble compounds with silver halide or substances which reduce the silver halide or compounds which can form developer nuclei (e.g. sodium sulphite).

These materials used with developer fluids have the disadvantage that they separate out only with difficulty, especially in conjunction with gelatin. The image quality is thus adversely affected. To avoid this disadvantage, it is known in an improved method to replace the gelatin partly or wholly with other film forming substances, such as cellulose derivatives, polyamides, polyesters, polyvinyl alcohols, polyvinyl acetate, partially hydrolized polyvinyl acetate, polyvinyl acetals, or other synthetic or natural resins. These materials are also included in the receiving layer of the present invention.

Furthermore, light-sensitive layers are known in which the latent image is developable by the action of heat and these layers, which are normally based upon gelatin, also contain materials which form silver nuclei or rednction nuclei on illumination (exposure). The diffusion is effected by the release of water of crystallization which takes place by heating substances which give off their water crystallization to temperatures below their melting point. Gelatin behaves reversibly as regards Water absorption and itself is taken up by part of the water of crystallization which is formed.

Furthermore, a method is known in which the ditiusion is discontinued by a heating effect and in which use is made of an image-receptor material, which is formed of non-reversible polyvinyl alcohol and contains no silver nuclei. The invention relates to a further im provement of this method, but is not exclusively limited thereto.

It is to be noted that the last-mentioned diffusion process, which is discontinued by a heating effect and pro ceeds without a developer bath, is of extreme economic importance, since the apparatus required is of reduced complexity and cost and the manufacture of prints is greatly facilitated. From this standpoint, the basic method with an image-receptor material without silver nuclei is to be considered as being of particular importance, since this material can be made much more cheaply and is more stable in use than the substances which are required for ordinary dry methods.

In the material used in the dry process with a heating effect, moisture must be available in a form which is dissipated in use by the heating effect. Such materials must be transportable and stable over long time periods and they must be able to Withstand the most varied operative conditions as regards atmospheric humidity and ambient temperature. Even if a package can be made substantially airtight in order to exclude such influences to the greatest possible extent, it still means that a considerable amount is expended in the manufacture of the packaging and also that there is a loss of time involved in opening a package for the purpose of using the material containing it. This time can be considerable in individual cases, apart from the added expenses due to the considerable packaging costs. It is to be noted that the materials used for carrying out the silver diffusion process tend to separate out in the layers, either in the form of Water of crystallization or in chemical combination with various amounts of moisture, which dry out from or are otherwise evolved in or by the film support.

The invention has the object of improving the materials used heretofore in the heating step of a dry process, as regards stabilization of the moisture content, so that under constant conditions at least the same good behavior is attained as in the normal fluid process.

This problem is solved in accordance with the invention in that an image-receiving material is used which has on a sheet-like support at least one sensitive layer, at least one of the layers applied to the support including at least one of the following hygroscopic salts: zinc chloride hemihydrate, lithium chloride monohydrate, potassium acetate, calcium chloride dihydrate, zinc nitrate hexahydrate and potassium carbonate hexahydrate. in conjunction with a photographic-film former.

According to a preferred embodiment, an imagereceiving material is used which has on the support two successively applied layers, namely the so'called base or adhesive layer, which advantageously contains at least one of the stated salts, and the image-receptor layer, which preferably contains the substances required for image formation. In this connection, it may be mentioned that a part of the substances belongings to the imagereceptor layer can also be located in the base or adhesive layer in separate form. Furthermore, a particular embodiment provides that at least one of the aforementioned hygroscopic salts can be provided only in the image-receptor layer insofar as it is applied exclusively to the support. The various additives mentioned have a long-range moisture-stabilizing effect, combined with the property of the greatest water irnpermeability, so that particularly in the use of the base or adhesive layer any drying out of the image-reception layer through the image carrier is reliably prevented.

The problem of regulation of moisture content has already been investigated with materials which are sensitized, i.e., made light-sensitive, by electrostatic charging, particularly when paper sheets are to be used in that process. It has been discovered that the completely dry paper base of such a sheet does not hold a latent electrostatic image. It is known to disperse a hygroscopic salt in such a paper sheet, whereupon photo-conductive layers may be applied to such paper sheet, if required. In this use, no moisture remains in the photoconductivelayers associated with the paper sheet, so that the problem to which the invention is directed, namely to stabilize the moisture content in a definite way which is associated with the reaction layers, does not occur. Surprisingly, it has been found that the additives used in electro-photography in connection with a protective colloid also provide such a moisture-stabilizing effect in the heating process with the materials for the silver diffusion process, so that these materials have a considerably improved holding power as compared with known materials.

According to a preferred feature of the invention, a receptor material is used which embodies polyvinyl alcohol as the film former.

A particular feature of the invention consists in arranging the base layer on the back of the film support, namely on the side away from the image-receptor layer. This has the advantage that, on stacking the paper, the moisture in the image-receptor layer cannot migrate into the overlying sheet. The base or adhesive layer acts primarily as a moisture-impervious barrier.

A further improvement in the material as regards stabilisation of the moisture content is provided in accordance with the invention in that the layers include one or more amino acids. Of particular advantage are those amino acids which are readily soluble in water, such as glycine, leucine, tyrosine and the like, although good results can also be obtained with other amino acids. A further improvement of the silver diffusion process carried out with the heating step is obtained, particularly in connection with the substances added for moisture sta bilization, in that the image-receptor layer includes substances which produce compounds which are difiiculty soluble in the inter-diffusing complex silver salt. Such substances, NaCl for example, have previously not been included in the image-receptor layer. They also lead to a further increase in the density of the image obtained. It may be mentioned that this is particularly so with a material which includes polyvinyl alcohol as the film former in the imagereceptor layer and does not contain any silver nuclei. Such image-receptor layers are described for example in my co-pending application Ser. No. 176,806 filed on Feb. 14, 1962, for Non-Reversed Positive Prints, now abandoned, and it may be mentioned that, within the scope of the invention for improving the moisture stabilization, use may be made of the receptors which are described in the aforesaid copending application. The supports consist of a material, e.g. a paper, which is suitably permeable for the diffusion process.

4 For carrying out the invention, use may be made of a receptor material which includes a base layer as Well as an image-receptor layer according to the following examples.

Example 1 A photographic paper is provided with a base layer of the following composition:

1st layer:

Polyvinyl alcohol g 10 H O ml 250 Potassium acetate g 20 2% solution of a wetting agent, e.g.

Mirasol ml.... 15

The potassium acetate is a hygroscopic organic salt. On this base layer, after drying, a second layer of the following composition is applied:

This layer thus likewise contains potassium acetate as the hygroscopic organic salt, whereby a better moisture reserve is attained. One example of co-pending application Ser. No. 176,806 contains sodium acetate as a plasticizer for the polyvinyl alcohol. This sodium acetate has no moisture-stabilizing effect similar to that of potassium acetate.

Furthermore, the receptor layer contains, in addition to the known and ordinary substances, sodium chloride for forming a difficultly soluble compound with the complex silver salt.

Example 2 The same as Example 1, except for the further addition of an amino acid, namely 0.5 g. of glycine in the base layer.

Example 3 The same as Example 2, except for the further addition of l g. of cellulose powder to the base layer. This cellulose powder has the object of improving the bond between the two layers.

Example 4 The base layer is according to Example 1 and the second layer likewise is according to Example 1, with the substitution of an amino acid for the 1 g. zinc oxide and 1 g. aluminum oxide contained in Example 1, namely 0.5 g. of leucine. The moisture stabilization and intensity of the image obtained are improved.

Example 5 The base layer according to Example 1 is modified in that, instead of the 15 mls. of Mirasol provided as a wetting agent, 1 g. of hydroxybenzoic ethyl ester is provided.

It has further been found that, in the preparation of the image-receptor layers for silver diffusion methods, homogeneous and more readily handled layers are obtained if the second layer, that is the image-receptor layer according to Example 1, contains emulsions prepared as follows.

In a flask (for example a distillation flask), the desired layer colloid, for example polyvinyl alcohol, is stirred with a plasticizing agent, e.g. glycerol or glycol. To the requisite amount of water to be added, the further additives are admixed in the order given in the example and are then stirred with the colloid. A reflux condenser is added and refluxing is carried out for about one hour. The emulsion is then taken out and dried in the usual way. The amount of the layer is made in such a thickness that in the dry state it measures from to microns.

The image formation by the heat process, the exposed negative layer and the image-receptor layer are brought into contact and are intimately pressed together between rollers, preferably under a light pressure, the temperature being increased to the region of to 90 C. for a sufiicient length of time or the process being repeated until the desired image formation is achieved.

The invention is therefore operative with receptors according to the aforesaid application Ser. No. 176,806 and includes the substances according to that disclosure.

The development of a dry silver diffusion process has given rise to the problem of providing a process which not only has the advantage of avoiding liquid developers, in comparison with the known wet process, but also gives excellent prints with the same rapidity. This additionally gives rise to the problem of obtaining a finished print which, despite the presence of substances which split of]? water of crystallization in the reception emulsion, is a product having a surface which does not give any impression of the presence of moisture.

For this purpose a positive emulsion is used which is formed from polyvinyl alcohol and is devoid of silver nuclei and to which there are added, in addition to the dihydric or trihydric alcohols known to be reducing agents, other reducing agents which are known in photographic practice as substances which reduce silver halide or form development nuclei. These are, for example, developer substances and/or sodium sulphite which simultaneously act to protect the reducing agents from oxidation.

The invention not only utilises a much more rapid reaction and hence shortens the time for the production of a print, but at the same time gives a much better density.

It is extremely advantageous to use substances which are reducing agents known as developer substances in photographic practice, for example hydroxylamine compounds of aromatic hydrocarbons, and, in particular, (i.e. hydroquinone It has also been found that the quality and mode of operation of the positive emulsion used in this heat process can be improved by adding to these emulsions small quantities of water-soluble thermoplastic vinyl resins. In this case use is advantageously made of substances which, by virtue of reactive groups (for example OH-groups), are water-soluble, have a low reducing power, and are compatible with the emulsion former of the positive emulsion (polyvinyl alcohol). Such substances are the polyglycols, preferably polyethylene glycol. Water-soluble thermoplastic cellulosic resins such as methyl celluloses or cellulose glycol ethers can also be used with equal success in place of the water-soluble thermoplastic vinyl resins.

When used in special proportions, these additives enable the available water of the positive emulsion formed from polyvinyl alcohol to be regulated both before and after processing. This results in the advantage that the product obtained is surprisingly dry for a heat process; this effect could not be expected in view of the well-known use of polyvinyl alcohol to improve the separation of gelatin emulsions processed by the wet method, as stated in the introduction.

A further advantage of these additives is that they permit, inter alia, a thinner application of emulsion, so that the production of the material is rendered less expensive and its processing is facilitated.

Examples of the positive or reception emulsion according to the present invention are given below.

After coating on a foil and drying, the resultant positive is heated in close contact with an exposed negative containing developer substances.

An emulsion support in the form of a foil, for example of paper, is used for the coating and drying. Heating is effected between 50 and C. until development of the image in the reception emulsion is completed.

The polyvinyl alcohol used has a viscosity of 28:4 cp. at 20 C. (determined in a 4% aqueous solution), a sa ponification number of 20:15 in mg. KOH per g., a hydrolysation degree of 97.5-99.5, a pH value of about 5, a bulk weight of 350450 and a specific gravity of 1.2 1.35.

The positive emulsion of this example contains hydroxylamine hydrochloride as an additional reducing agent, in a ratio of 1:20 with respect to the polyvinyl alcohol emulsion former. This is preferably a lower limit and larger quantities of the additional reducing agent may advantageously be added. In this connection, it should also be pointed out that the ratio of 50 ml. water to 0.5 g. of additional reducing agent is an advantageous ratio which is preferably modified by the addition of more reducing agent.

Example 7 Positive emulsion:

Polyvinyl alcohol (as described in Example 6) grams 10 Water ml 50 Glycerol ml 15 crystallized sodium acetate grams 5 Aluminum hydroxide gram 0.2 Dry soda grams 2.0 Dry potassium metabisulphite gram 1.0 Hydroxylamine hydrochloride do 0.5 Dry sodium sulphite do 0.5

After coating on a foil and drying, this emulsion is heated in close contact with an exposed negative containing developer sub-stances as described in Example 6.

In the positive emulsion of this example, dry sodium sulphite is provided as a special protective agent for the additional reducing agent.

Example 8 Postive emulsion:

Polyvinyl alcohol (as described in Example After coating on a foil and drying, this positive is heated in close contact with an exposed negative containing developer substances as described in Example 6.

Hydroxylamine hydrochloride and p-aminophenol hydrochloride are added as reducing agents in this case. This example has a ratio of additional reducing agent to poly- 7 vinyl alcohol of about 1:8.5, which is greater than the above-indicated advantageous lower limit of Example 6.

Example 9 Positive emulsion:

Polyvinyl alcohol (as described in Example 6) grams 10 Water ml 50 Glycerol ml 15 Tylose (reg. trademark) gram 1 Crystallized sodium acetate "grams-.. 5 Dry soda do 2 Aluminum hydroxide gram 0.2 Dry potassium metabisulphite do 1.0 Hydroxylamine hydrochloride do 1.0 P-aminophenol hydrochloride do 0.2 Dry sodium sulphite do- 0.5

6) grams 10 Water ml 50 Glycerol ml Tylose gram 1 Polyglycol do 1 Crystallized sodium acetate grams 5 Dry soda do 2 Aluminum hydroxide gram 0.2 Dry potassium metabisulphite do 1.0 Hydroxylamine hydrochloride do 1.0 P-aminophenol hydrochloride do 0.2 Dry sodium sulphite do 0.5

After coating on a toil and drying, this positive is heated in close contact with an exposed negative containing developer substance as described in Example 6.

In this example, the efiect produced by the addition of Tylose as described in Example 9 is reinforced by the addition of a polyglycol, such as a polyethylene glycol having an average molar weight of 13,000 to 17,000, a solidification point of about 60 C., a viscosity of 1,000 to 1,500 cps. at C. (determined in a 50% aqueous solution) and a hydroxyl number of 6.6-8.6 in mg./g. KOH.

Example 11 Positive emulsion:

Polyvinyl alcohol (as described in Example 6) grams 10 Water ml 100 Glycerol do 15 Tylose grams 2 Crystallized sodium acetate do 10 Dry soda do 4 Dry potassium metabisulphite gram 1 After coating on a foil and drying, this positive is heated in close contact with an exposed negative containing developer substances as described in Example 6.

The addition of dry potassium metabisulphite is an example of an additional complex former which can also be used in the formulae given in Examples 6 and 10.

It is to be understood that, in Examples 6 to 11, one of the aforementioned hygroscopic salts is also present and that if required the agents given in the examples for carrying out the method can be mutually interchanged.

I claim:

1. A sheet of image-receiving material for the dry production of unreversed positive prints by juxtaposition with a sheet bearing an exposed photographic silver-halide emulsion layer and heating of the sheets upon such juxtaposition, said sheet of image-receiving material comprising a support; a base layer on said support having a polyvinyl-alcohol matrix containing a moisture-stabilizing agent in the form of a hygroscopic salt selected from the group which consists of zinc chloride hemihydrate, lithium chloride monohydrate, potassium acetate, calcium chloride hexahydra-te, zinc nitrate :hexahydrate and potassium carbonate dihydra-te; and a receiving layer on said base layer having a polyvinyl-alcohol matrix containing silver-halide solvent and developer together with sodium acetate.

2. The image-receiving material, defined in claim 1 wherein said base layer further includes at least one amino acid selected from the group which consists of glycine, leucine and tyrosine.

3. The image-receiving material defined in claim 2 wherein said hygroscopic salt and said amino acid are present in said base layer in a weight ratio of the order of 40: 1, and said matrix and said base layer in a weight salt are present in said ratio of the order of 1:2.

4. A sheet of image-receiving material for the dry production of unreversed positive prints by juxtaposition with a sheet bearing an exposed photographic silver-halide emulsion layer and heating of the sheets upon such juxtaposition, said sheet of image-receiving material comprising a support; a base layer on said support having a polyvinyl-alcohol matrix containing a moisture-stabilizing agent in the form of a hygroscopic salt selected from the group which consists of zinc chloride 'hemihydrate, lithium chloride monohydrate, potassium acetate, calcium chloride hexahydrate, zinc nitrate hexahydrate and potas sium carbonate dihydrate; and a receiving layer on said base layer having a polyvinyl-alcohol matrix containing silver-halide solvent and developer together with a moisture-releasing agent selected from the group which consists of zinc chloride hemihydrate, lithium chloride monohydrate, potassium acetate, calcium chloride hexahydrate, zinc nitrate hexahydrate, potassium carbonate dihydrate and sodium acetate, one of said layers further containing an amino acid selected from the group which consists of glycine, leucine and tyrosine.

References Cited UNITED STATES PATENTS 2,698,237 12/1954 Land 9629 2,759,825 8/1956 Land 9629 2,834,676 5/1958 Stanley ct-al. 9629 3,042,514 7/1962 Roth 9629 3,080,230 3/1963 Haydn et a1. 9676 3,248,219 10/1966 Jacobs 96-76 FOREIGN PATENTS 1,261,098 4/1961 France.

789,837 1/1958 Great Britain.

OTHER REFERENCES Chemical Abstracts, vol. 39, p. 669, 1945.v

The Condensed Chemical Dictionary 5th ed., 1956, pp. 528 and 659, pub. by Reinhold Pub. Corp, New York City.

DONALD LEVY, Primary Examiner. 

